An optical waveguide mixes and directs light emitted by one or more light sources, such as one or more light emitting diodes (LEDs). A typical optical waveguide includes three main components: one or more coupling elements, one or more distribution elements, and one or more extraction elements. The coupling component(s) direct light into the distribution element(s), and condition the light to interact with the subsequent components. The one or more distribution elements control how light flows through the waveguide and is dependent on the waveguide geometry and material. The extraction element(s) determine how light is removed by controlling where and in what direction the light exits the waveguide.
When designing a coupling optic, the primary considerations are: maximizing the efficiency of light transfer from the source into the waveguide; controlling the location of light injected into the waveguide; and controlling the angular distribution of the light in the coupling optic. One way of controlling the spatial and angular spread of injected light is by fitting each source with a dedicated lens. These lenses can be disposed with an air gap between the lens and the coupling optic, or may be manufactured from the same piece of material that defines the waveguide's distribution element(s). Discrete coupling optics allow numerous advantages such as higher efficiency coupling, controlled overlap of light flux from the sources, and angular control of how the injected light interacts with the remaining elements of the waveguide. Discrete coupling optics use refraction, total internal reflection, and surface or volume scattering to control the distribution of light injected into the waveguide.
After light has been coupled into the waveguide, it must be guided and conditioned to the locations of extraction. The simplest example is a fiber-optic cable, which is designed to transport light from one end of the cable to another with minimal loss in between. To achieve this, fiber optic cables are only gradually curved and sharp bends in the waveguide are avoided. In accordance with well-known principles of total internal reflectance light traveling through a waveguide is reflected back into the waveguide from an outer surface thereof, provided that the incident light does not exceed a critical angle with respect to the surface. Specifically, the light rays continue to travel through the waveguide until such rays strike an index interface surface at a particular angle less than an angle measured with respect to a line normal to the surface point at which the light rays are incident (or, equivalently, until the light rays exceed an angle measured with respect to a line tangent to the surface point at which the light rays are incident) and the light rays escape.
In order for an extraction element to remove light from the waveguide, the light must first contact the feature comprising the element. By appropriately shaping the waveguide surfaces, one can control the flow of light across the extraction feature(s) and thus influence both the position from which light is emitted and the angular distribution of the emitted light. Specifically, the design of the coupling and distribution surfaces, in combination with the spacing (distribution), shape, and other characteristic(s) of the extraction features provide control over the appearance of the waveguide (luminance), its resulting distribution of emitted light (illuminance), and system optical efficiency.
Hulse U.S. Pat. No. 5,812,714 discloses a waveguide bend element configured to change a direction of travel of light from a first direction to a second direction. The waveguide bend element includes a collector element that collects light emitted from a light source and directs the light into an input face of the waveguide bend element. Light entering the bend element is reflected internally along an outer surface and exits the element at an output face. The outer surface comprises beveled angular surfaces or a curved surface oriented such that most of the light entering the bend element is internally reflected until the light reaches the output face
Parker et al. U.S. Pat. No. 5,613,751 discloses a light emitting panel assembly that comprises a transparent light emitting panel having a light input surface, a light transition area, and one or more light sources. Light sources are preferably embedded or bonded in the light transition area to eliminate any air gaps, thus reducing light loss and maximizing the emitted light. The light transition area may include reflective and/or refractive surfaces around and behind each light source to reflect and/or refract and focus the light more efficiently through the light transition area into the light input surface of the light-emitting panel. A pattern of light extracting deformities, or any change in the shape or geometry of the panel surface, and/or coating that causes a portion of the light to be emitted, may be provided on one or both sides of the panel members. A variable pattern of deformities may break up the light rays such that the internal angle of reflection of a portion of the light rays will be great enough to cause the light rays either to be emitted out of the panel or reflected back through the panel and emitted out of the other side.
Shipman, U.S. Pat. No. 3,532,871 discloses a combination running light reflector having two light sources, each of which, when illuminated, develops light that is directed onto a polished surface of a projection. The light is reflected onto a cone-shaped reflector. The light is transversely reflected into a main body and impinges on prisms that direct the light out of the main body.
Simon U.S. Pat. No. 5,897,201 discloses various embodiments of architectural lighting that is distributed from contained radially collimated light. A quasi-point source develops light that is collimated in a radially outward direction and exit means of distribution optics direct the collimated light out of the optics.
Kelly et al. U.S. Pat. No. 8,430,548 discloses light fixtures that use a variety of light sources, such as an incandescent bulb, a fluorescent tube and multiple LEDs. A volumetric diffuser controls the spatial luminance uniformity and angular spread of light from the light fixture. The volumetric diffuser includes one or more regions of volumetric light scattering particles. The volumetric diffuser may be used in conjunction with a waveguide to extract light.
Dau et al U.S. Pat. No. 8,506,112 discloses illumination, devices having multiple light emitting elements, such as LEDs disposed in a row. A collimating optical element receives light developed by the LEDs and a light guide directs the collimated light from the optical element to an optical extractor, which extracts the light.
A.L.P. Lighting Components, Inc. of Niles, Ill., manufactures a waveguide having a wedge shape with a thick end, a narrow end, and two main faces therebetween. Pyramid-shaped extraction features are formed on both main faces. The wedge waveguide is used as an exit sign such that the thick end of the sign is positioned adjacent a ceiling and the narrow end extends downwardly. Light enters the waveguide at the thick end and is directed down and away from the waveguide by the pyramid-shaped extraction features.
Low-profile LED-based luminaires have recently been developed (e.g., General Electric's ET series panel troffers) that utilize a string of LED components directed into the edge of a waveguiding element (an “edge-lit” approach). However, such luminaires typically suffer from Fow efficiency due to losses inherent in coupling light emitted from a predominantly Lambertian emitting source such as a LED component into the narrow edge of a waveguide plane.
Smith U.S. Pat. Nos. 7,083,313 and 7,520,650 disclose a light direction device for use with LEDs. In one embodiment, the light direction device includes a plurality of opposing collimators disposed about a plurality of LEDs on one side of the device. Each collimator collimates light developed by the LEDs and directs the collimated light through output surfaces of the collimators toward angled reflectors disposed on a second side opposite the first side of the device. The collimated light reflects off the reflectors out of and out of the device from the one side perpendicular thereto. In another embodiment, the collimators are integral with a waveguide having reflective surfaces disposed on a second side of the waveguide, and the collimated light is directed toward the reflective surfaces. The light incident on the reflective surfaces is directed from the one side of the device, as in the one embodiment.
Dau et al. U.S. Pat. No. 8,410,726 discloses a lamp for use in an Edison-type screw-in connector. The lamp includes a plurality of LED modules oriented radially within a base. In one embodiment, each LED module has a wedge shape. LEDs located near the base of the module emit light into a light guiding and extracting wedge. Surface extraction features are introduced into the wedge to extract light. A user can operate the light with different combinations of modules to generate a desired light output from the lamp.
Summerford et al. U.S. Pat. No. 8,547,022 discloses a lighting control system having a primary high intensity discharge light source and a secondary LED light source. Power is routed to either the primary or the secondary light source by a common power source.
Beeson et al. U.S. Pat. No. 5,396,350 teaches a backlighting apparatus used for flat panel electronic displays. The apparatus includes a slab waveguide that receives light from a light source positioned adjacent a side surface thereof and an array of microprisms attached to a face of the waveguide. Each microprism has a side surface tilted at an angle from the direction normal to the surface of the waveguide. Light emitted from the microprisms is substantially perpendicular to the slab waveguide.
Zimmerman et al. U.S. Pat. No. 5,598,281 discloses a backlight assembly for electro-optical displays. Light emitted from a light source disposed within a reflector travels through an array of apertures and is collimated by an array of tapered optical elements aligned with the array of apertures. Microlenses may be disposed adjacent the optical elements to further collimate the light. The surfaces of the optical elements are planar or parabolic in shape.
Zimmerman et al. U.S. Pat. No. 5,428,468 teaches an optical illumination system for applications that require substantially collimated light. The system comprises a waveguide that receives light at an edge thereof. An array of microprisms is attached to one face of the waveguide. Each microprism has at least two sidewalls tilted at an angle from the normal of the surface of the waveguide. An array of microlenses may be disposed atop the array of microprisms to further collimate the light.
Steiner et al. U.S. Pat. No. 5,949,933 discloses an optical illumination system for collimating light. The system includes a waveguide that receives light at an edge thereof and an array of lenticular microprisms attached to one face of the waveguide. Each microprism has a light input surface optically coupled to the waveguide and a light output surface opposite the input surface. The light input surface includes a number of tapered grooves perpendicular to the length of the lenticular microprism. The system also includes an array of microlenses to further collimate the light.
Hou et al. U.S. Pat. No. 5,839,823 teaches an illumination system including a light source adjacent to or housed within a reflector. A light-directing assembly having at least one microprism carried on a base wall is positioned adjacent the light source opposite the reflector. The microprism may be polyhedronal, curvilinear, and polyhedronal curvilinear. A lens array may be disposed on the other side of the base wall.
Kuper et al. U.S. Pat. No. 5,761,355 discloses a light directing optical structure comprising a waveguide having a multiplicity of prisms attached thereto. Light redirected by the prisms is constrained to a range of angles. The side face(s) of the prisms may be planar or curved. An array of lenses may be used to spread the light output of the prisms to a wider distribution angle.